Redox amplification processes have been described, for example in British Specification Nos. 1,268,126, 1,399,481, 1,403,418 and 1,560,572. In such processes, color materials are developed to produce a silver image (which may contain only small amounts of silver) and are then treated with a redox amplifying solution (or a combined developer-amplifier) to form a dye image.
The developer-amplifier solution contains a color developing agent and an oxidizing agent that will oxidize the color developing agent in the presence of the silver image which acts as a catalyst.
Oxidized color developer reacts with a color coupler to form the image dye. The amount of dye formed depends on the time of treatment or the availability of color coupler and is less dependent on the amount of silver in the image as is the case in conventional color development processes.
Examples of suitable oxidizing agents include peroxy compounds including hydrogen peroxide and compounds that provide hydrogen peroxide, e.g., addition compounds of hydrogen peroxide; cobalt (III) complexes including cobalt hexammine complexes; and periodates. Mixtures of such compounds can also be used.
The image-forming step can be followed by a stop bath, bleach and fix, although the bleach and/or fix may be omitted if the silver coating weight of the material processed is low enough. Recently it has been proposed that the bleach bath may contain a peroxide as sole bleaching agent. Such proposals have carried the warning that redox amplification has to be stopped before bleaching otherwise color staining will occur due to image formation continuing in the peroxide bleach solution.
There is a continuing need to reduce photographic processing times. This is desirable as it means that processing throughput can be increased. The customer is equally pleased because he can see the results a little sooner.